X-ray high-order refinements of hydrogen atoms: a theoretical approach

Recent work in X-ray crystallography has demonstrated that reasonable nuclear H positional parameters can be obtained by refinements using high-order data only. A theoretical model for high-order refinements of H atoms has been developed which simulates the experimental results. For a suitable choice of the lower sin θ/λ cut-off, the H atoms are shown to refine to their actual nuclear positions. The calculations imply that the proper cut-off is indeed dependent on the type of atom to which the H is bonded, in agreement with experimental results.